Isaiah Washington as Preston Burke
In season three, Burke abandoned Cristina at the altar and then just took off, eventually winning a Harper Avery award elsewhere and then at some point, moving to Zurich, Switzerland to open his own hi-tech hospital. He got married, started a family, and then in season 10, he invited Cristina to his hospital to take it over for him as he retired.
Isaiah Washington left the series after it was reported that he called costar T.R. Knight a gay slur during an argument on set, and all his defenses just kept making it worse before he finally was let go from the series. Apparently he and ABC made up, because they let him return for a second in 2014. His most significant role since was as Thelonious Jaha on The CW’s The 100, until his character died in season five.